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Sunday, April 27, 2014
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Solve Decision-Making Expression using Logical Operators in JAVA

4:23 AMSunday, April 27, 2014
Relational operators often are used with logical operators (also known as conditional operators sometimes) to construct more complex decision-making expression. The Java programming language supports six conditional operators-five binary and one unary-as shown in the following image.


The logical OR operator (||)

The logical OR operator (||) combines two expressions which make its operands. The logical OR (||) operator evaluates to Boolean true if either of its operands evaluate to true.

This principle is used while testing evaluating expressions. Following are some examples of logical OR operation:

  • (4= =4) || (5 = =8)    results into true because first expression is true.
  • 1 = = 0 || 0 > 1         results into false because neither expression is true (both are false).
  • 5 > 8 || 5 < 2            results into false because both expression are false.
  • 1 < 0 || 8 > 0            results into true because second expression is true.

The operator || (logical OR) has lower precedence than the relational operators, thus, we don’t need to use parenthesis in these expressions.

The logical AND operator (&&)

The logical AND operator, written as &&, also combines two expressions into one. The resulting expression has the value true only if both of the original expression (its operands) are true. Following are some examples of AND operator (&&).

  • (6 == 3) && (4 == 4)           results into false because first expression is false.
  • (4 == 4) && (8 == 8)           results into true because both expressions are true.
  • 6 < 9 && 4 > 2                     results into true because both expressions are true.
  • 6 > 9 && 5 < 2                     results into true because both expressions are false.

Because logical AND operator (&&) has lower precedence than the relational operators, we don’t need to use parentheses in these expressions.

The logical NOT operator (!)

The logical NOT operator, written as "!", works on single expression or operand i.e. it is a unary operator. The logical NOT operator (!) negates or reverses the truth value of the expression following it i.e. if the expression is true, then expression is false, and vice versa.

Following are some examples of logical NOT operation:

  • ! (5 ! = 0) results into false because 5 is non zero (i.e., true)
  • ! (5 >2) results into false because the expression 5>2 is true.
  • !(5>9)  results into true because the expression 5>9 is false.

The logical negation operator "!" has a higher precedence then any of the relational or arithmetic operators. Therefore, to negate an expression, you should enclose the expression in parentheses:

!( x > 5 ) will reverse the result of the expression x > 5
    Whereas! x > 5 is equivalent to ( ! x ) > 5

i.e., it will first reverse the truth value of x and then test whether the reverse of x’s truth value is greater than 5 or not.

Relational Operators in JAVA
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